1. Field of the Invention
The present invention relates generally to electric arc saws, and more particularly to an improved electric arc saw blade construction.
2. Description of the Prior Art
The use of electric arc saws to cut metallic work pieces has been known for some time. Such saws operate by electrically melting a kerf into the work piece, normally by providing a rotating blade and applying an electrical potential between the blade and the work piece. The rotating blade is moved across the work piece at an appropriate distance so that the electric current flows between the periphery of the blade and the work piece to cause the melting. Rotation of the blade assists in removing the melted material from the kerf, preventing the buildup of molten metal between the blade and the bottom of the kerf and preventing a localized reheating of the blade.
A number of early patents issued in the field of electric arc sawing. See, for example, U.S. Pat. Nos. 1,701,919; 2,015,415; 2,059,236; 2,355,838; and Re. 20,035. While these patents suggested the great potential of electric arc sawing, years passed before that potential was commercially realized. One of the first commercially successful electric arc saws is described in Schlienger, U.S. Pat. No. 4,399,344. In addition to the apparatus, these patents describe methods for optimizing operating parameters in order to maximize cutting efficiency under a variety of different conditions.
The mechanical systems of the electric arc saw, including drive, slip ring assembly, power supply and controls are now well developed. Extended use of electric arc saws, however, has revealed drawbacks common to prior art devices relating to blade technology and design. Blades of typical electric arc saws, for example the one disclosed in Schlienger et al. U.S. Pat. Ser. No. 4,519,368, may rotate at speeds as fast as 40 m/sec, thereby subjecting the blade to large centrifugal forces. In addition, the high operational temperature associated with the cutting process subjects the blade to temperature deformation. Finally, magnetic attraction between the blade and the work piece may subject the blade to significant lateral forces. A major drawback common to blades operating under such conditions is that the structural integrity required of high speed blades precludes the use of materials having optimal magnetic, thermal and electrical conductivity because such materials normally have insufficient strength properties.
During cutting it is crucial that the blade remain flat at all times to assure accuracy of the cut, to avoid side arcing caused by blade deformation resulting in the blade passing too close to the side wall of the kerf, to avoid binding of the blade in the kerf and to avoid permanent dishing of the blade caused by continuous stress. Constructing the blade of a high strength material such as steel ensures that the blade remains flat in operation. However, such materials usually neither have the desired high electric conductivity in the area where arcing occurs nor the desired high thermal conductivity to avoid thermal deformation and localized heating which can cause blade pitting and an ablation of the cutting edge of the blade.
Another drawback common to prior art electrical arc saw blades is blade economy and life span. Given the centrifugal, thermal, magnetic, frictional and related stresses on a blade, a reduction of blade wear is a primary concern. The cost of manufacturing the blade with the optimum qualities for cutting performance is substantial, thus it is highly desirable to minimize the frequency of blade replacement, yet not sacrifice cutting performance.
Heretofore, most electric arc saw blades have comprised a thin metallic disk having a substantially continuous circular periphery. A number of modifications to this basic configuration have been proposed. Such proposals include forming the entire blade from discrete arc sections, for example the Russian patent of Vniktistalkonstrukt Ser. No. SU-621-512, the selective coating and removal of coating on a blade, for example, U.S. Pat. Ser. No. 2,526,423 of D. W. Rudorff, and attaching inserts to the periphery of a blade, as in Japanese Pat. Ser. No. 43-22835 of Ebigawa Denki. No proposal, however, directly addresses the present objects of maximizing strength, performance and life span and optimizing the magnetic thermal and electrical conductivity characteristics of an electric arc saw blade.